How can I stop the world from leaking?

My FTB Direwolf20 server is leaking!

2013-04-11 22:29:24 [SEVERE] [ForgeModLoader] Detected leaking worlds in memory. There are 4 worlds that appear to be persisting. A mod is likely caching the world incorrectly
2013-04-11 22:29:24 [SEVERE] [ForgeModLoader] The world 6e929b52 (world) has leaked.
2013-04-11 22:29:24 [SEVERE] [ForgeModLoader] The world 28db4ccf (world) has leaked.
2013-04-11 22:29:34 [WARNING] [Minecraft] Can't keep up! Did the system time change, or is the server overloaded?

This is on a server I've just started up. What can I do?

Solution 1:

According to this Feed the Beast forum, it is related to the loading and unloading of worlds. This applies to an issue Forge is having with the ChickenChunks mod because of the way it unloads worlds. Try going to your Advanced Java Options in the launcher (options --> Advanced options) and entering -XX:MaxPermSize=256m -XX:PermSize=128M in the Additional Java Perimeters field.

Linking to enough Mystcraft worlds and Twilight Forest multiple times can also be the cause of severe memory leaks. There also exists a semi-rare bug with causes FML (Forge ModLoader) to leak memory no matter what you do. Another common solution is to disable all of the wireless redstone mods, such as RedPower 2 and WRCBE. Basically, if you had made any Twilight Forest and Mystcraft worlds before, it is likely to happen.

Direwolf20 gives his two cents about the problem here:

Solution 2:

Tell the mod author, there's nothing you can do (or should do) about this issue.

When mods work with different dimensions (nether, the end etc.) they often leave certain chunks loaded accidentally. This isn't normally a problem, but if lots of your mods are doing it (and with many dimensions, thanks mystcraft) it can cause quite bad memory leaks.

Just one mod doing this isn't a problem, so ignore it, and maybe bug the mod author to fix their small coding error.